The tape bearing surface of magnetic tape heads contain the transducers that read and write data to and from a magnetic tape. In magnetic disk heads, this surface is referred to as the air bearing surface. Tape bearing surfaces and air bearing surfaces of common thin film magnetic heads generally consist of three regions, a substrate, a thin film region that contains the magnetic transducers, and a closure. Each region is made up of one or more materials that have a variety of characteristics such as resistance to media wear, machinability, magnetic properties, electronic properties, corrosion resistance, ease of deposition, and ease of thin film pattern definition. Substrates and closures are usually made of hard, nonmagnetic materials. The bulk of each thin film region is formed with a nonmagnetic insulator. Pole tips and shields consist of "soft" magnetic materials. (In this context, "soft" magnetic material means that the material demagnetizes rapidly.) While read transducers consist of a very thin layer of a magneto-resistive material.
Friction between the magnetic medium and the magnetic head causes the tape bearing surface to wear. Characteristic differences in the various tape bearing surface materials result in uneven wear. In particular, the substrate and closure materials generally wear slower than the thin film and magnetic materials. Over time, a gap forms between the magnetic media and the transducers. This phenomenon is called pole tip recession. Gaps as narrow as 60 nanometers can make a magnetic head ineffective. Pole tip recession becomes more acute as magnetic field strengths are reduced to record higher information densities in the magnetic medium.
Past approaches to control pole tip recession have attempted to maintain a planar tape bearing surface. The theory being that if all of the materials wear at the same rate, pole tip recession will not take place. These approaches have had limited success because the varied magnetic, electrical, mechanical and chemical constraints placed on the materials prevent the selection of materials with a uniform wear rate.